The present invention generally relates to an apparatus for recording and reproducing signals, and more particularly, to an apparatus for recording and reproducing video signals and audio signals, such as a VTR (Video Tape Recorder).
Generally, in recent years, in the video/audio signal recording and reproducing apparatus such as the VTR, the picture quality and the sound quality have been improved by converting the conventional analog recording to digital recording. In digital recording, the information content of the signals to be recorded is greater than that of analog recording.
The provision of narrower recording tracks is one benefit of digital recording. As the digital recording is different from the analog recording, the S/N does not depend upon the track width. However, one factor for determining the track width depends upon whether or not the error rate necessary for complete correction can be sufficiently obtained. That is, digital recording may result in a considerably narrowed track width as compared with analog reading, but one must consider when determining the track width the accuracy required during editing operations (insertion editing and so on). During editing, a partial track may be cut or reduced since complete continuity cannot be effected with respect to the original recording at the editing points due to a difference in the linearity between different machines or due to tracking errors. As such, it is necessary to set the track width to obtain a sufficient error rate.
As a conventional embodiment, recently disclosed is a D-2 composite digital VTR (The Journal of the Institute of Television Engineers of Japan, Vol. 42, No. 5, 1988, p. 498-p. 502) for broadcasting. In the conventional embodiment, the recording track having a width of 39 .mu.m is composed of a pair of heads, without the provision of a guard band, having mutually different azimuth angles, so that the output may not be reduced even when track shift has occurred due to interchangeability and so on through the reproducing operation using a head which is greater in width than the recording track. In the editing operation, signals are written over top one another on the already recorded track, with no erasing head being provided (overwriting).
Track cutting and interference at the editing point resulting in the case where the editing operation is effected by overwriting as in the conventional embodiment will be discussed below.
FIG. 6 illustrates the condition where the track 2 is overwritten on the already recorded track 1 from the point An Also, the oblique lines in the tracks 1, 2 denote the azimuth angles of the respective heads. FIG. 6(a) depicts a condition Where the overwriting head is shifted to the right by the width Te. FIG. 6(b) depicts a condition where it is shifted to the left by the width Te. The track pitch is Tp.
In the case as shown in FIG. 6(a), the signal components of the width Tp are reproduced at the editing point through the reproduction using the wider heads, but the signal from the track of the width Te is mixed as an interference signal of the azimuth which is the same as that of the track immediately after the editing point. The signal of the same azimuth is not attenuated, thus resulting in interference of the normal signal. The signal from the original track Tp is equivalently reduced by this interference. Now assume that the reduction portion by the interference of the track Te is kTe (1&lt;k.ltoreq.2). If the recorded signal is of the unit sine wave, k equals 1. As the recorded signal contains components of a wide frequency range (from a low frequency to a high frequency), k becomes 1 or between 1 and approximately 2.
The equivalent effective track width Ts1 at this time becomes as follows. EQU Ts1=Tp=kTe (1)
In the case shown in FIG. 6(b), the already recorded track immediately before the editing point is cut by the width Te. Accordingly, the effective width Ts2 of the track becomes as follows. EQU Ts2=Tp-Te (2)
The tolerance track shift amount Te at the time is such that a sufficient value is provided of the error rate in the effective track width. Assume that the effective track width is Ts, Ts2 becomes greater,than Ts1 from equations (1), (2). EQU Ts=Ts1 (3)
The width Te for satisfying the equation (3) becomes the tolerance track shift amount. From equations (1), (3), EQU Te=(Tp-Ts)/k (4)
In the conventional embodiment, the track shift amount at the editing point becomes an interference as it is. It is thus necessary to widen the normal track width more than is otherwise necessary with respect to the track shift at the editing point. This results in a lessening of the recording time per unit area of the tape, an increase in the size of the cassette housing the tape, and an increase in the operating costs. Thus, from this point of view, it is desirable to have a record format wherein the track pitch itself is made as small as possible, and wherein the tolerance value of the track shift at the editing time with respect to the track pitch is made as large as possible.